Update docs for readthedocs

[RayOei]

Readthedocs is again syncing (#740) and shows some updates are needed:

• Alignment of the menu seems off
• Travis is deprecated and needs removing
  • Include Github actions link or something informational in Travis replacement?
• Topics menu doesn't seem to navigate to anything
• Chapter menu doesn't seem to navigate to anything
• align index.rst with readme.rst
  • banners
  • check references
  • check URL's
  • remove IRC
• more ...?

[vassilit]

https://github.com/sahib/rmlint/pull/721